The present invention relates to a charged particle beam irradiation method and a charged particle beam apparatus.
Conventionally, when an insulator workpiece is observed or processed by a charged particle beam, such as an ion beam or electron beam, the irradiation beam is raster scanned and positioned on the workpiece. Raster scanning is how to sequentially irradiate an array of points.
FIG. 7 shows a raster scan-based processing of a workpiece. As shown in FIG. 7, when the workpiece is processed, the charged particle beam is applied to the center positions of the pixels that are on a contour line of a process area as well the pixels within the process area (the process area means the area which is to be processed from now on) that are not on the contour line. A pixel used herein is a minimum unit area for beam irradiation and an area divided in the horizontal (X) and vertical (Y) directions at an interval corresponding to a minimum unit of irradiation beam deflection. However, in general, since the process area is not always rectangular, especially when the contour line of the process area is a diagonal line that overlies pixels across two rows, a step is unfortunately formed halfway through the process pattern contour, which should be a straight line.
As a technology to solve the above problem, there has been proposed a beam irradiation method in which a process area is expressed as raster data by displacing the position of a specific contour line such that the contour line can be expressed as a straight line and the bit map is displaced by the same amount in the opposite direction (see, for example, JP-A-6-214376).
FIG. 8 shows a processing method using this technique. In the figure, the diagonal contour line is displaced such that the contour line will not included in pixels in the same row, thereby preventing step generation halfway through the process pattern contour.
When a process area has multiple contour lines for which step generation should be avoided, the method described in the patent document 1 has limited applications because the offset positions at which step generation can be avoided for the contour lines do not always coincide. This method is also problematic in that a contour line that should be diagonal becomes vertical or horizontal, and although a contour line for which a step has been eliminated becomes more accurate, other parts may become less accurate.
The invention has been made in view of such situations and aims to provide a charged particle beam irradiation method and a charged particle beam apparatus capable of improving accuracy of process pattern contour lines independent of the shape of a process area of a workpiece.